Magnetic fluid seals in magnetic clutches



Oct. 15, 1957 E. G. PERRY 2,809,733

MAGNETIC FLUID SEALS IN MAGNETIC CLUTCHES Filed Oct. 29. 1952 3 Sheets-Sheet 1 L mi;

( FLU/D LEVEL INVENTOR MM w w ATTORNEYS Oct. 15, 1957 E. e. PERRY 2,809,733

MAGNETIC FLUID SEALS IN MAGNETIC CLUTCHES Filed Oct. 29, 1952 3 Sheets-Sheet 2 1N VENTOR ATTORNE Y5 Oct. 15, 1957 E. G. PERRY MAGNETIC FLUID SEALS m MAGNETIC CLUTCHES 3 Sheets-Sheet 5 Filed Oct. 29, 1952 w :4, w 3 NM T x N Q a 6 .4 5 6 .J Mm 6 AA/A/ 0 II II & 1 w 44 BY Maw United States Patent MAGNETIC FLUID SEALS 1N MAGNETIC CLUTCHES Edward Gordon Perry, Dallas, Tex., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Application October 29, 1952, Serial No. 317,531

14 Claims. (Cl. 192-215) This invention relates to magnetic seals in magnetic clutches and like apparatus employing a magnetizable medium such as a fluid or material.

Magnetizable mediums are generally composed of a metallic powder such as iron powder alone or suspended in some fluid, such as an oil, with the characteristics which most nearly meet the working conditions of the clutch. This magnetic material or fluid is put into the clutch in what is known as the working gap. The portions of the clutch forming the working gap are composed of magnetic material to form magnetic poles on either side of the working gap. A torque cup or disc is attached to an output shaft which is supported by the clutch housing in bearings so that the torque cup or disc will be free to rotate in the working gap.

Whenever a signal is applied to the clutch from any external source such as a permanent magnet or a signal coil, the flux produced passes from one pole to the other through the working gap and hence through the magnetizable medium. This causes the iron particles to become magnetized and to line up or stiffen in the direction of the flux. As the magnetic fluid stiflens, it produces an increase in the coupling torque between the cup and the clutch housing which constitutes the driving member of the clutch. Thus the output shaft will rotate or tend to rotate, it restrained, in the direction of the clutch housing rotation. It can be seen that if the output shaft is restrained and the clutch housing rotates, the torque cup must disturb or break the alignment of these magnetic force lines. As these lines of force are broken the shearing forces and heat generated tends in time to break down the magnetic fluid and cause the oil to evaporate. if enough of the fluid evaporates the iron powder concentration will become greater and result in erroneous measurements of applied signals.

Another effect that may be obtained when a signal is applied to the clutch is that stray magnetic forces may attract the iron powder out of the working gap. The effect of iron powder leaving the working gap is twofold; the first is that the iron powder may get into the output shaft bearings and cause them to foul or even bind and, the second is that the magnetic fluid concentration is weakened which, as in the case of too great a concentration, results in erroneous measurement of applied signals.

Accordingly, it is an object of this invention to provide a means to combat the tendency for the magnetic fluid to become either weakened or concentrated by the eflect of magnetic fields, high temperatures, shearing forces, or other factors influencing magnetic fluids.

it is a further object of this invention to provide a magnetic seal to prevent iron filings from leaving the working gap of the clutch by controlling the fluid level and the magnetic path across the working gap.

It is another object of this invention to provide a reservoir of magnetic fluid outside of the working gap, provide seais to prevent the iron filings from getting into the bearings and to keep the fluid circulating so that the working life of the fluid will be prolonged.

It is a still further object of this invention to provide a means to keep the iron filings or particles out of the bearings and in the working gap and to provide a supply of clean oil which will compensate for any evaporation of. the oil in the magnetic fluid mixture.

it is another object of this invention to provide a magnetic seal for a clutch whereby the clutch will operate more efficiently, economically, and accurately than has heretofore been possible.

Other objects and advantages of the present invention will become readily apparent from a detailed consideration of the following description when taken in conjunction with the drawings in which:

Figure l is a sectional view in elevation showing the magnetic seal of the present invention as applied to a magnetic fluid clutch having an external field core and signal coil;

Figure 2 is a sectional view in elevation showing the magnetic seal of the present invention as applied to a magnetic fluid clutch having a built-in signal coil;

Figure 3 is a sectional view in elevation showing a further arrangement of the magnetic seal of the present invention as applied to a magnetic fluid clutch;

Figure 4 is a sectional view in elevation showing a modified form of the magnetic seal of the present invention as applied to an output shaft of a magnetic fluid clutch; and

Figure 5 is a view in section taken along line 5-5 of Figure 4.

Figures 1, 2 and 3 show different types of clutches for the specific purpose of illustrating that the magnetic seal of this invention is not confined to only one type of clutch construction. Figure 1 represents a clutch to which signals are applied from an external field core and signal coil. The magnetic material in the clutch is arranged to apply the flux generated by the signal across the working gap and to complete the circuit with the surrounding field core. The clutch in Figure 2 shows the signal coil built into the clutch. External signals are applied to the signal coil through collector rings with the magnetic circuit being completed within the clutch. The clutch shown in Figure 3 has the signal applied in the same manner as the clutch in Figure l, the major difference in construe tion being that in Figure 3 the magnetic fluid acts on a torque disc rather than a torque cup.

The method of applying operating signals to the clutches, such as the external field core and signal coil as shown in Figure l or the coil within the clutch as shown in Figure 2, is a separate principle and is well known in the art. It forms no part of the present invention and is to be distinguished from the steady state flux means which constitutes part of the magnetic seal of the present invention.

Referring now to the drawings, the clutch housing for a magnetic fluid clutch as shown in Figure l is composed of a lower housing section I joined to a driving shaft 35 and an upper housing section 2 joined to lower housing section 1 by a ring 3. Hub 5 joins a torque cup 4 to an output shaft 6 which in turn is supported in the housing section 2 by roller bearings 7 and 8 so that the output shaft is free to turn. The torque cup 4 extends down into the working gap 17. Leakage of magnetic fluid from the working gap 17 is prevented by means of a liner ring 15 and an 0 ring seal 16 located between the clutch rousing sections 1 and 2. A non-magnetic section 14 fits directly underneath the torque cup 4 to limit the magnetic path through the clutch to that portion of the clutch represented by the magnetic poles 20 and 21. The clutch as a Whole is supported by beatings and frame support sections indicated generally as 12 and 13 at 3 the bottom and top respectively, of the clutch. External signals to operate the clutch are applied through a field core 9 and signal coil 10. A permanent magnet 18, or if desired an electromagnet, is positioned to be separated from the clutch housing by air gaps 19.

In this particular clutch, magnetic fiuid fills the working gap to the point where magnetic pole 21 joins the non-magnetic material 14 and shown on the figure by the fluid level line. Flux from the north poleN of permanent magnet 18 crosses the air-gap l9 to pole 2g} flows, from pole 26 through the working gap 17 to the other magnetic pole 21 and completes the circuit by crossing air-gap 19 at the south pole S of permanent magnet 28. The flux path is indicated as 5%. This flux, crossing the working gap 17, causes the fluid to become magnetized which in turn exerts a very strong force on the magnetic particles to keep them in the working gap 17. Thus any tendency for the iron particles to get up into the bearings 7 and 8 by virtue of operation of the clutch is prevented. The proper placement of nonmagnetic material 22 will eliminate stray flux currents which tend to pull the iron powder out of the working gap.

The clutch shown in Figure 2 is similar to the clutch of Figure 1, but shows the signal coil 10 built into the clutch housing sections 1 and 2, the fluid level in a reservoir 32 above the working gap 17, and a cavity 23 splitting magnelc pole 2%? into two pole parts 2.9a and Operating signals for coil 9 are transmitted through collector rings 32 and conductors 33 connected to coil 9. Pole part a bounds the working gap 17 and pole part 2% bounds the reservoir 32. Flux from the pole N of permanent magnet 18, as before, crosses the gap 19 to magnetic pole 2! but in this clutch the magnetic flux is divided into two paths. One of the flux paths is traced from pole 29:: across the working gap 17 to pole 21 and then completes its path back to the south pole S of magnet 18. This flux path is indicated as 51. The flux in pole 20a has no influence on the fluid above the working gap 17 since the increased reluctance of the air gap above the top of pole 21 plus the shielding effect of non-magnetic material 14 does not allow flux to cross over and thus magnetize the fluid. Therefore, it is necessary to supply an additional magnetic seal to control the fluid above the top of pole 21. This additional magnetic seal is supplied by the second flux path which is traced from pole 20b across to the torque cup 4 at point in the vicinity of hub 5. By taking advantage of the fact that the magnetic potential of the cup 4 is half-way between the magnetic potential of the poles 2t and 21 of the working gap, the flux from 29b to point 3% can complete its path by traveling down the cup 4 to pole 21 and back to the permanent magnet 18 at the south pole S. This flux path is indicated as 52. Any magnetic fluid which reaches this magnetic seal in the vicinity of the hub 5 will thus be magnetized at that point and iron powder prevented from getting into the bearings 7 and 8. Cavity 23, which splits the magnetic pole 20 prevents the passage leading to bearing 8 from ever becoming submerged regardless of the angle to which the clutch is tilted and is useful as a means of filling the clutches during assembly. This clutch has the advantage that the life of the fluid is extended since the reservoir provides a reserve fluid supply for circulation in the working gap and therefore, no particular portion of the fluid is worked continuously. Holes 31 drilled in the torque cup 4 allow for filling the working gap 17 and for circulation of the fluid.

Figure 3 represents a further modification of the use of a steady state flux source to provide a magnetic seal and therefore keep iron particles from migrating out of the working gap and into the bearings. As stated before, this clutch shown in Figure 3 is very similar to the one shown in Figure 1 with the exception of a flat ltorque. disc 4 and a .corresponding flat working gap 17.

the shaft depending upon the direction of rotation.

2,809,733 p a r r 4 In addition to' the permanent magnet 18 which generates a flux path 53 from north pole N through pole 20, working gap 17, pole 21, and back to the south pole S, the clutch is also provided with two helices 24 and 25. Helix 24, which is formed as a part of the output shaft 6, can be either a right-hand or left-hand thread. Helix 25 can also be formed'with either a right-hand or lefthand thread. However, it is preferred that the two threads 24 and 25 are formed oppositely; that is, if helix 2-: is right-hand thread, then helix 25 is a lefthand thread. Helix 24 is inside of helix 25 and the crowns of the threads cross each other at a number of points along their axial lengths. Since both helices are made of magnetic material, a flux path 54 is generated through them from permanent magnet 18. Since the closer crossing points at the crowns have a lower reluctance than the thread roots or now-crossing points at the crowns, high intensity fields are created at these points. if there is a relative motion between the two helices, the position of the cross points producing the high intensity field will travel up or down the axis of If magnetic particles are in the presence of this type of field, they will tend to be carried along with the high intensity field. Thus there will be set up a definite pumping action. This pumping action of the helical magnetic field is pronounced enough for a definite separating action to take place so that liquid can flow through the field in one direction while magnetic particles are forced against the flow of the fluid in the other direction. In this clutch, the helical seal is a continuous part of the working gap 17. With the working gap 17 arranged in this manner, the magnetic particles entering between the helices 24 and 25' will be pumped back into the magnetic fluid in gap 17 to keep a constant iron-oil ratio instead of permitting the particles to pile up at a point outside of the gap 17. Another advantage of this helical pumping and sealing arrangement is that a reservoir of clean oil can be maintained around the output shaft 6 in the area indicated as 28. A cup ring seal 29 can be arranged at the top of the clutch to prevent spilling of the fluid should the clutch he inverted. Any loss of oil by evaporation can be taken care of by the surplus oil in the reservoir 28.

Figures 4 and .5 show a modification of the magnetic seal as applied to the output shaft 6. In this particular arrangement the clutch housing section 2 is provided with a helix 40 and shaft 6 is provided with a plurality of vertical splmes 41. The operation of this arrangement will be similar to the two helices shown in Figure 3 in that a downwardly traveling magnetic field will be established between the helix 40 and splines 41 to pump the magnetic particles back into the working gap 17. It 1s, or course, appreciated that the helix 40 can be on shaft 6 and the splines 41 on the clutch housing section 2.

It is also possible to employ a helix on clutch housing section 2 slmilar to helix 40 with the smooth cylindrical outer surface of shaft 6. In this instance, the crowns of the helix and the corresponding points on the shaft 6 will have a 'lower reluctance than the thread root portions of the helix and their corresponding points. Thus a high intensity field will be created at these points which can be made to travel downwardly upon the proper selec tion of the direction of rotation of the helix, thereby creating a definite pumping action to return the particles to working gap 17 while permitting the fluid to pass into the area 28. Also, the helix can be instead on the shaft 6 and can be made to cooperate with the smooth cylindrical bore of the clutch housing section 2 which surrounds the shaft 6 in this area.

If desired an electromagnet can be used in place of permanent magnet 18 which supplies the flux to operate the magnetic seals as above described. The use of an electromagnet will have the advantage of providing a control over the strength of the flux.

It is quite apparent that the use of the permanent magnet 18 or an electromagnet in the manner above described will result in a bias being placed on the clutch. This, of course, is desirable in clutches in a push-pull arrangement or for any other reason. However, oftentimes it is desirable to operate a clutch without a bias. In these cases a ring magnet can be built into the housing section 2 around the pair of helices of Figure 3 or the helix 40 and vertical splines 41 of Figure 4. Thus, the effective ness of the magnetic seal and pump will be preserved without unduly interfering with the normal operation of the clutch.

Also the same result can be accomplished by any other means that would effectively apply a magnetic flux to the magnetic trap (the pair of helices of Figure 3 or the helix 4% and vertical splines 41 of Figure 4) with or without applying a bias to the clutch. For example, a series of small bar magnets can be spaced around the trap or a magnetic path can be established around the trap and a permanent or electromagnet can be placed adjacent to the path. In the latter arrangement the permanent or electromagnet can be shielded from the working gap, if desired. Thus it can be seen that any means can be employed as long as the means functions to apply a suitable magnetic flux to the magnetic trap.

While the present invention has been described with reference to magnet fluid clutches, its use with magnetic particle clutches very broadly is quite apparent and such use is not to be precluded in any way. For example, this invention would operate on a clutch in which only iron powder is used.

While this invention has been shown and described in conjunction with specific embodiments, nevertheless, various changes and modifications obvious to one skilled in the art are within the spirit, scope, and contemplation of the present invention.

What is claimed is:

1. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, further magnetic flux means to apply a bias across said space, and particle sealing means associated with said space designed to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

2. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, a perma nent magnet acting as a further magnetic flux means to apply a bias across said space, and particle sealing means associated with said space designed to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

3. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, an electromagnet acting as a further magnetic fiux means to apply a bias across said space, and particle sealing means associated with said space designed to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

4. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, further magnetic flux means to apply a bias across said space, and particle sealing means including helical threads formed on at least one of said members associated with said space to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

5. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, further magnetic flux means to apply a bias across said space, and particle sealing means including helical threads formed on both of said members associated with said space to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

6. In .a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, further magnetic flux means to apply a bias across said space, and particle sealing means including oppositely formed helical threads on said members associated with said space to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

7. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, further magnetic fiuX means to apply a bias across said space, and particle sealing means including helical threads formed on one of said members and splines formed on the other of said members associated with said space to establish in cooperation with said further magnetic fiux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

8. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic fiux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, a ring magnet acting as a further magnetic flux means to apply a bias across said space, and particle sealing means associated with said space designed to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

9. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said members communicating with said working gap, a plurality of bar magnets acting as a further magnetic flux means to apply a bias across said space, and particle sealing means associated with said space designed to establish in cooperation with said further magnetic flux means a traveling magnetic field in saidspace during normal operation of said clutch that moves in die direction of said working gap to drive particles entering said space toward said Working gap.

10. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, one of said members being formed by a torque element connected to a shaft bearing mounted in the other member, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said shaft and said other member communicating with said working gap, further magnetic flux means to apply a bias across said space, and particle sealing means associated with said space designed to establish in cooperation With said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

11. In a magnetic clutch including a driving member and a driven member having a Working gap defined therebetween, one of said members being formed by a torque element connected to a shaft bearing mounted in the other member, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined etween said shaft and said other member communicating with said working gap, further magnetic flux means to apply a bias across said space, and particle sealing means characterized by helical threads formed on at least one of said shaft and said other member adjacent said space to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

12. In a magnetic clutch as defined in claim 11 the further improvement of said particle sealing means being characterized by helical threads being formed on both of said shaft and said other member.

13. In a magnetic clutch including a driving member and a driven member having a working gap defined therebetween, one of said members being formed by a torque element connected to a shaft bearing mounted in the other member, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said shaft and said other member communicating with said working gap, further magnetic flux means toapply a bias across said space, and particle sealing means characterized by helical threads formed on one of said shaft and said other member and splines formed on the other of said shaft and said other member associated with said space to establish in cooperation wit said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said working gap to drive particles entering said space toward said working gap.

14. In a magnetic clutch including a driving member and a driven member having a Working gap defined therebetween, one of said members being formed by a torque element connected to a shaft bearing mounted in the other member, magnetically permeable particles in said working gap, and magnetic flux means to couple said members, the improvement comprising a space defined between said shaft and said other member communicating with said Working gap, a permanent magnet acting as a further magnetic fiurr means to apply a bias across said space, and particle sealing means associated with said space designed to establish in cooperation with said further magnetic flux means a traveling magnetic field in said space during normal operation of said clutch that moves in the direction of said Working gap to drive particles entering said space toward said working gap.

References Cited in the file of this patent UNITED STATES PATENTS 2,519,449 Findley Aug. 22, 1950 2,557,140 Razdowitz June 19, 1952 2,587,077 Winther Feb. 26, 1952 2,601,961 Stephenson July 1, 1952 2,614,668 Waderlow et al Oct. 21, 1952 2,651,754 Perry et al Sept. 8, 1953 2,663,809 Winslow Dec. 22, 1953 2,713,927 Rabinow July 26, 1955 2,725,133 Winther Nov. 29, 1955 2,748,911 Stahl June 5, 1956 FOREIGN PATENTS 976,917 France Nov. 1, 1950 OTHER REFERENCES Technical Report 1213, National Bureau of Standards, Washington, D. C. Copy received in Div. 68 on March 30, 1948, 192Magnetic Fluid Material.

Magnetic Fluid Clutch, Product Engineering, April 

